1. Field of the Invention
The present invention relates to techniques for manufacturing visual tags or makers. More specifically, the present invention relates to techniques for producing low-visibility retroreflective visual tags.
2. Related Art
A relatively inexpensive technique for identifying an object and for determining the position of an object in the physical world is to attach a Radio Frequency Identification (RFID) tag to the object. RFID tags are relatively small and inexpensive, and generally do not require a power source. Because of these advantages, RFID tags (although mostly of the battery-powered “active” variety) are widely used in numerous applications as diverse as inventory-control systems, and electronic toll booths on freeways.
However, existing unpowered “passive” RFID tag readers cannot pinpoint the exact location of an object. Rather, they simply report the presence or absence of a tag in their field of sensitivity. Moreover, RFID tag readers only operate at short range. They also function badly in the presence of metal, and interfere with each other when many tagged objects are present.
Some of these problems can be overcome by using active RFID technology or similar methods, such as ultrasound. However, these techniques require expensive, power-consuming electronics and batteries, and they still may not determine position accurately when attached to dense or metallic objects.
Visual tag-based methods do not have the same problems, but the task of recognizing visual tags is itself a complicated problem, which requires a large amount of computation. Consequently, existing systems have difficulty distinguishing tags from complex backgrounds or handling variable lighting. They also require too much computational power to be practical in many applications. Moreover, large, visually-prominent tags, which are easier to recognize, are not aesthetically pleasing, and are consequently unsuitable for many applications.
Hence, what is needed is a method and an apparatus for identifying and/or determining the position of an object without the above-described problems of existing systems.